1. Field of the Invention
The present invention relates to scanner. More specifically, the present invention relates to a scanner that controls stepping motor torque.
2. Description of the Prior Art
Computers have become increasingly ubiquitous in almost all aspects of life, from home to office. With the growth of computers, the requirements of personal image processing are increasing. Scanners are therefore becoming more and more popular. And, for catering to the various image requirements of users, scanners have to offer the users various resolution options. When using a scanner, users can choose a suitable resolution to scan documents or pictures. For example, when a user generates icons for a homepage, he or she will choose a lower scanning resolution. For high quality digital images, a higher resolution will be chosen.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a function block diagram of a prior art scanner 10. FIG. 2 is a schematic circuit diagram of the scanner 10 of FIG. 1. The scanner 10 comprises a scanning module 12, a stepping motor 16, and a control circuit 18. The scanning module 12 is used to scan a document and generate image data. The control circuit 18 controls the stepping motor 16 to generate a torque for driving the scanning module 12. As shown in FIG. 2, when control circuit 18 drives the scanning module 12, it applies a voltage to the stepping motor 16, activating the stepping motor 16. When the stepping motor 16 operates in a steady-state condition, the current of the stepping motor 16 is fixed, and the torque of the stepping motor 16, thus, is fixed. A consequence of this is that, when the scanning module 12 scans the document at a high resolution, the stepping motor 16 generates a surplus torque that causes excessive noise and shock. This excessive noise and shock influences the quality of the image generated by the scanner 10.
It is therefore a primary objective of the present invention to provide a scanner that controls the torque of the stepping motor. The scanner uses a suitable torque when scanning a document.
In a first embodiment of the present invention, the scanner comprises a scanning module for scanning a document, a driving module for driving the scanning module, and a control circuit for controlling the scanner. The driving module comprises a stepping motor for driving the scanning module forward and backward. The control circuit controls the current of the stepping motor and thus controls the torque that the stepping motor produces.
In a second embodiment of the present invention, the control circuit further comprises a driving program, a processor for executing the driving program, and a memory for storing a torque table. The torque table records a plurality of torque values. Each of the torque values corresponds to a predetermined condition when the stepping motor produces a torque. When the driving program is executed, the driving program chooses one of the torque values according to the predetermined condition, and transmits a driving signal to the driving module. The stepping motor of the driving module generates a suitable torque according to the driving signal, and then drives the scanning module.
It is an advantage of the present invention that the stepping motor of the scanner generates a suitable torque to drive the scanning module according to a resolution that the scanning module uses. Therefore, the stepping motor does not generate excessive torque.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.